2.1. Introduction
Transitional cell carcinoma (TCC), also referred to as urothelial carcinoma (UC), is the most common urinary tract neoplasm in the dog. This form of cancer may be localized in one or more anatomical sites, including the kidneys, ureters, urinary bladder, prostate, and urethra, with most cases being detected in the bladder [1]. In the bladder, the cancer develops from the transitional epithelial cells that form the lining of the bladder and invade into the bladder wall and layers of muscle. As the mass becomes larger a frequent consequence is obstruction to the flow of urine, either from the kidneys to the bladder, or from the bladder through the urethra. Pathology assessment of canine TCCs indicates that most are higher grade tumors that have the ability to spread to lymph nodes and other organs in the body (lung, liver, others).
The American Veterinary Medical Association estimates that 4.2 million dogs are diagnosed with cancer each year in the US. While precise lifetime risk and incidence numbers for TCC in the overall pet dog population is not known, TCC is estimated to represent ˜1-2% of all diagnosed cancers, indicating that as many as 40,000-80,000 dogs each year could develop TCC in the US. In addition there are several breeds of purebred dog that have been reported to have an elevated risk of developing TCC of the bladder, including Scottish terrier, Shetland sheepdog, West Highland white terrier, Wire/Fox terrier and beagle.
2.2. The Diagnostic Challenge of Canine TCC
A major challenge to diagnosis of TCC in a dog is that the symptoms of urothelial cancer in the dog are shared with variety of other urinary tract conditions. For example, bladder infections, bladder stones, hyperplastic growths in the bladder, and inflammation of the bladder can all cause symptoms in the dog similar to those resulting from a bladder cancer. Evaluation of canine urine by routine cytology may be misleading, since the non-malignant conditions above may cause shedding of abnormal looking cells in the urine, which may be mistaken for a malignancy. The use of imaging techniques, such as radiography and ultrasonography, may identify the presence of unusual growths in the urinary tract, but these may or may not be malignant, and may also result in the presence of abnormal looking cells in the urine. Presently, a confirmed diagnosis of a canine TCC may be made only following the evaluation of a biopsy of the tumor by a pathologist. Obtaining a biopsy of a probable mass in the urinary tract may be performed during surgery, cystoscopy or by traumatic catheterization, which have a decreasing level of intervention, respectively. However, any procedure that disturbs the likely tumor mass may result in seeding of malignant epithelial cells elsewhere on the local area, resulting in spreading of the cancer. The chances of ‘seeding’ are of concern to the clinical management. Confirmation of diagnosis of a TCC in dogs presenting with symptoms suggestive of a TCC would thus be desirable from an assessment of a free catch urine sample.